The ink-jet recording method has come into practical use in which droplets of a recording liquid containing a water-soluble dye, e.g., a direct dye or an acid dye, are issued from a minute ejection orifice to conduct recording.
With respect to the recording liquid, it is required not only to rapidly fix to recording paper for general business use, e.g., paper for electrophotography or other PPCs (plain-paper copiers) and fanfold paper (continuous paper for computers, etc.), to give a print in which the printed characters are of good quality, that is, the printed characters (image) are free of blurring and have clear outlines, but also to have excellent storage stability. Therefore, usable solvents for the recording liquid are severely restricted.
With respect to dyes for the recording liquid, they are required, for example, not only to have sufficient solubility in the restricted solvents as described above and be stable even in long-term storage of the recording liquid, but also to give printed images having a high density and excellent water and light resistance. However, it has been difficult to satisfy these many requirements simultaneously.
Although various techniques (as described, e.g., in JP-A-61-101574 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-61-101576, JP-A-61-195176, JP-A-61-62562, JP-A-61-247771, JP-A-62-156168, JP-A-62-246974, JP-A-63-63765, JP-A-63-295685, JP-A-1-123866, JP-A-1-240584, JP-A-2-16171, JP-A-3-122171, JP-A-3-203970, and JP-A-4-153272) have hence been proposed, all these prior art techniques have failed to sufficiently meet the requirements of the market.
In JP-A-4-279671 (U.S. Pat. No. 5,262,527) and PCT International Publication WO 94/16021, dyes usable in ink-jet recording are disclosed which have a structure comprising two molecules of a triazinyl-containing monoazo dye which are bonded together through a divalent organic connecting group; such a structure is similar to the structure of the dye for use in the present invention described hereinafter.
However, in the former reference (JP-A-4-279671), there is a description to the effect that the divalent organic connecting groups are not important. The examples of the connecting group which are given therein include a (substituted) phenylenediamine group, and differ from the connecting group in the present invention. The dye having the connecting group whose structure is planar lacks in insufficient coloring property, so that resulted images become to have insufficient color densities.
These groups also have a drawback that-since they are conjugated groups, the dyes containing these groups have a deep and strongly bluish color tone. Further, there is a description therein to the effect that the triazinyl-bonded group (represented by Z in the reference, which corresponds to X.sub.1 or X.sub.2 in the present invention) is preferably a group bonded to the triazinyl group through a nitrogen atom, e.g., NHC.sub.2 H.sub.4 OH or morpholino, and the structures of the dyes used in the Examples given in that reference are limited to those having the group. However, such a dye gives images with reduced chroma.
The divalent organic connecting group used in the latter reference (WO 94/16021) is a group derived from either a (substituted) phenylenediamine group or a substituted piperazine group and is hence different from the connecting groups in the present invention. However, the divalent organic connecting group derived from a (substituted) phenylenediamine is undesirable as described above, while use of the divalent organic connecting group derived from a substituted piperazine results in the dyes of insufficient resistance to light and water.